Synchronizing, regulating, and controlling receivers and generators



'A .26, 1930, v R. V.-L'.- HARTLEY 1,774,003

smcanomzme, REGULATING, AND CONTROLLING RECEIVERS AND GENERATORS Original Filed Sept. 8, 1917 I Patented Aug 26, 1930 I UNITED STATES .PATENT' OFFICE RALPH V.-L. HARTLEY, OF EAST ORANGE, NEW JERSEY,.ASSIGNOR TO WESTERN- EREC- TRIC COMPANY, INCORPORATED, NEW YORK, N. Y., A GORPORATION'OIB" NEW SYNCHRONIZING, REGULATING, AND CONTROLLING RECEIVERS AND GENERATORS Application filed September 8, 1917, Serial No. 866,440. Renewed March 16, 1920.

' erator at a receiving station with the generator of a co-operating transmitting station. In that type of system for radio telephony or carrier telephony on wires in which the received carrier wave consisting of modulated high frequency oscillations is combined with high frequency oscillations from a local oscillator of the same frequency as the carrier wave, it isessential for eflicient reception of the signals that the two high frequencies should be identical orsubstantial- Since variations in frequency of the local generator are as effective in causing departure from synchronism as variations in frequency of the distant generator, the invention is equally adapted to prevent departures from synchronism due to either of these causes. In case the distant generator varies, the local generator is affected so as to case the frequency of the distant generator remains constant, the local generator is caused to react upon itself so .as to prevent any dearturc from synchronism. The arrangements described herein, whereby a generator is caused to react-upon itself so as to prevent variations in frequency or other characteristics of its output Waves from occur ing, constitute important features of the invention.

However, certain other principlesand fea- 'tures of the invention are of general application and may be utilized, for example, in controlling the frequency of heterodyne 0s cillators or controlling or synchronizing for any purpose a generator in accordance with changes in, the condition of other apparatus at the same or a communicating station. Among the important features of the invention are the provision of improved means vary in a corresponding manner, while in for and methods'of synchronizing electrical wave producing devices, maintaining a constant relation between a transmitting and a receiving oscillator in signaling and other wave transmission systems, controlling one generator b another, controlling generatorsand other evices by the differential action of circuits oppositely arranged with respect to a controlled device, controlling apparatus by the conjoint action of currents representing sum and difference frequencies, causing an electron discharge generator or oscillator to be self-controlling, regulating a generator by applying a portion of the output energy to a tuned circuit and utilizing the varying current in the tuned circuit for controlling the generator, controlling the output of a high frequency generator by the action of a circuit tuned to a frequency other than the frequency of the generator, and modulation of the output current of a generating or equivalent device in accordance with one or more other waves for control purposes.

A particular object of the invention is to provide means in systems of the kind herein described for causing the frequency of the locally generated oscillations to be identical at every instant of time with the received 1 frequency oscillations.

hi h 1 %)ther features and objects of the invention will beapparentfrom a perusal of the following detailed description and the appended claims.

While a complete system-embodying the invention is described, the various features thereof are not limited to application in any particular embodiment but may be utilized in various other systems for similar purposes.

In accordance with the herein described lated wave includes component waves of frequencies 12+ q, ;0- g, and g, of which the components 12+ g and p g are equal in amplitude. Hence it" is unnecessaryto give any verses its direction.

proof of this proposition. Assume that q isgreat .enough so that the frequencies p-l-g and p-g may be separated by suitably tuned circuits. Oscillations of frequency p+ 9 may then be impressed upon the input circuit of a suitable detector which also receives the incomingcarrier wave of frequency 12 One of the resulting component frequencies in the output circuit of the detector due to the unmodulated carrier wave would then be (gr-p Similarly the oscillations of frequenc p-g are impressed on another detector w ich also receives the carrier wave. One of the resulting components in the output of this)detector would be of the frequency q Eh irh of these component frequencies 9+ (gr-p and g- (12-10 is then caused to act upon a tuned circuit so adjusted that the frequency 9 is on the steep part of the resonance curve for the circuit. When, therefore, the quantity (p 39 departs from zero the current in one resonant circuit increases, and in the other decreases, the one to increase depending on the sign of p 12 In the output circult of the detectors associated with each resonant circuit a direct current is produced which corresponds to the unmodulated carrier component of the received currents, as

combined with the side band current from the local modulator. These direct currents vary with the changes in the frequencies p and 17 the direction of the variation being opposite in the two'circuits. The output circuit of each of the two latter-mentioned detectors includes means, such as a series inductance and a shunt condenser, for separating the detected currents due to the modulated carrier wave or other rapidly changing currents and leaving only the direct current due to the unmodulated' carrier wave.

These two currents are applied differentially to control the frequency of the local oscillator. One way of accomplishing this is to send the currents through two electromagnets so that they push in opposition on a magnet carried by a pivoted arm. This arm is adapted on being moved in one direction from its position of stable equilibrium to close an electrical circuit, thereby allowing current to flow therein; the arm on being moved in the opposite direction closes the electrical circuit so that the current also re- In this circuit is an electromagnet carried by an arm attached to the movable part of an adjustable condenser or inductance in the tuned circuit of the local oscillator. This last mentioned electromagnet is capable of being repelled or attracted by a stationary magnet. With such an arrangement, a variation from equality in frequency of the received currents and the locally generated oscillations will set up a force which will cause the pivoted arm to close the electrical circuit and energize the electromagnet carried by the arm of the adjustable impedance. According to the direction of this current this electromagnet will be regelled or attracted by the stationary magnet.

y suitable connections and adjustment of the various parts of the apparatus, the direction of motion of the arm may be made such as to decrease the frequency difference. The motion continues untilthe difference becomes zero, when'the moving force also becomes zero and the motion stops. In other words, the position ofsynchronism is a position of stable equilibrium.

For the better understanding of this invention reference is made to the following description, taken in connection with accompanying drawings, in which Fig. 1 illustrates an embodiment of this invention. Fig. 2 represents a modification thereof; and Fig. 3 is the resonance curve for a tuned circuit. In order to make the drawings more selfexplanatory, a reference character has been placed beside each audion to indicate its function. Thus A indicates that the audion is an amplifier; D indicates that it is a detector; Gr, an oscillation generator; M, a modulator; and U, a unidirectionally conducting device.

In Fig. 1 the vacuum tube 5 taken in connection with the inductance 6 and the-adtion generator of a well-known type. This generator impresses oscillations of frequency p upon the input circuit 9 of the modulator 10 by transformer 11. Oscillations of a fre quency q are also impressed on the input circuit 9 from the oscillation generator 13 by transformer 14. The resultant modulated oscillations in the output circuit 15 consist of oscillations of the frequencies 77+ g, p and p, as stated above. Assume that q is of such a value that p-l-q and p-q are sufliciently different that they may readily be separated by suitably tuned circuits. If the circuit 16, Which is connected to the outputcircuit 15 by transformer 17 is tuned to the frequency 12-9. the oscillations impressed on the input circuit 18 of the detector 21 by the transformer 22 are only of the frequency pg. Similarly, if the circuit 23 is tuned to a frequency p+q, then by the transformer 24, the input circuit 26 of the detector 27 will receive oscillations of only the frequency 9+1 These input circuits also receive carrier waves of frequency p which are incident upon the antenna 30. By the transformer 31, the received oscillations are impl essed on the tuned circuit 32 which in turn impresses them on the input circuits of the two unidirectionally conducting repeaters 34 and 35. By the transformers 37 and 38 the oscillations in theoutput circuits 39 and 40 are impressed on the detectors 21 and 27 respectively. It follows, therefore, that the currents resulting in the output circuits 42 and lllJ llll

. output circuits magnet 60 which is attached cuit 46 would be less,

43, due to the unmodulated component of the received currents, will contain components of frequencies q; (pp and q+ (ya-p respectively. y the transformers 44-and 45 these component frequencies are impressed upon two tuned circuits 46 and 47 respectively, both preferably tuned so that a frequency of the value g lies'on the steep part of the resonance curve for the circuits (see Fig. 3). The oscillations in these tuned circuits are impressed upon detectors 50 and 51. -The 53 and 54 of the detectors have direct currents which are de endent in intensity upon-the component requencies respectively. These direct currents are employed to energize two electromagnets 57 and 58 which are adapted to influence the pole to the pivoted arm 61. This arm on moving in one direction makes contact I D 63, thereby closing the electrical circuit 64 containing the battery 65 and the electromagnet 66. The arm 61 on moving in the opposite direction makes contact with the points 62 and 68, thereby closing the circuit containing the battery 69, which causes the current to flow through the electromagnet 66 in the direction opposite to that for the current from battery 65. This electromagnet 66 is carried by an arm 71'attached to the movable partof the condenser 7, the capacity of which determines the frequency of the oscillations generated by the oscillator 5. i If now the locally generated oscillations of frequency p have exactly the same frequency as the received carrier wave (p then the quantity (17-17 is zero, so thatthe two detectors 50 and 51 receive oscillations of the.

same frequency, namely 9. It follows, therefore, providing the detectors 50 and 51 have similar characteristics, that their output circuits have direct currents which are ,equal. The electromagnets 57 and 58 will then equally repel the magnet 60, so that the arm 61 would remain in the position of equilibrium without making contact with either the point 63 or the point 68. The setting of the condenser would remain ,the same. and the generator 5 would continue to generate oscillations of the same frequency.

However, if the frequency 79 isgreater than p then the frequency impressed on the tuned circuit 47 is greater than 9, so that the incident frequency would more nearly corre- 'spond to the frequency for resonance of said circuit, thereby giving rise to currents of greater intensity than for the frequency of just 9. The output circuit 54 would then have a larger direct current than when 2 equals 12 Similarly the currents in the tuned cirsince g 19-10 would be smaller. The current in the output circuit 53 would then be less than its former value.- The repulsion of the electromagnet 58 would then be greater than the magnet 57, so that stronger,

between the points 62 and upon-a suitable receiver 85.

the arm 61 would make contact with the point 68, closing the circuit 64 and causingthe stationary magnet 73 to' repel the magnet 66, so that the arm 71 moves clockwise, thereby increasing the capacity of condenser 7 and de- [the condenser setting would remain un' changed.

In a similar manner, if p is less than p the repulsion of the magnet 57 would be the so that the arm 61 would make contact between the points 62 and 63, thereby sending current in the circuit 64 in the direction opposite to that when p is greater than 12 The magnet 66- would then be attracted by the stationary magnet 73, so that there would be a counter-clockwise motion of the arm 71, a corresponding decrease in capacity and increase in frequency of the oscillations generated until the desired frequency and equality were .attained.

Such an arrangement as described above, therefore, provides means for synchronizing the locally generated oscillations with the oscillations received, thereby providing for efficient homodynereception. The oscillations of frequency p generated by the oscillator 5 are'impressed upon the input circuit of a unidirectionally conducting device 81, shown here to be. of the audion type. The oscillations in its output circuit are by transformer 82 impressed upon the detector 84. By the transformer 83, the detector also receives the modulated'carrier wave from the antenna. The detected currents may then be impressed The device 81 is inserted-so-that although oscillations may be transmitted from the oscillator 5 to the detector 84, oscillations may not pass in the opposite direction. The device thereby prevents oscillations from the antenna. from reacting upon the local oscillator.

It is true that the modulated as well as the unmodulated carrier waves would be impressed upon the tuned circuit 39, so that the output circuits of the detectors 50 and 51 would have rapidly varying currents, due to the detection of the modulated wave. However, the condenser 87 in the output circuit 53 provides a path of low impedance for these rapidly varying currents and'the choke coil 88 prevents these from energizing the electromagnet 57. Similarly condenser 89 and inductance 90 prevent the corresponding currents in the output circuit 54 from. energizingthe electromagnet 58. These rapidly varying currents will, therefore, not effect the setting of the condenser 7. As is well known, moving objects inthe neighborhood of the capacity 7 or coil 6, variations in ourrent's upply of generator G, or other causes, may tend to roduce variations in the frequency of osci lations produced thereby. Obviously, the system will act to restore departures from synchronisin due to variations in the frequency produced by the local generator as well as that of the distant generator. The above description of the synchronizing system is applicable, as shown, when both the modulated and unmodulated carrier waves are transmitted to the receiving station. The system, however, is operative, only less efiiciently when the unmodulated carrier wave is suppressed. If we assume that oscillations of only the frequencies p +g and p -g are transmitted, where 9 is the signal frequency at the transmitting station, then these incoming oscillations would be on one side combined with the locally modulated oscillations of p+g and on the other side with the oscillations of the frequency 21-9. The resulting low frequency oscillations in the first case would have the frequencies second case the low frequecies would be 9+91'(P P1) and 9 91* (2 1 1)- I the case previously described .the tuned 011- cuits 46 and 47 were tuned so that the frequency g was on the steep part of the resonance curve for the circuits. In this latter case either the frequency 9+9 or the frequency gg may be of such a value as to occur on the steep part of the curve. Having chosen one of the two frequencies, it is evident thatthe other, in the case of sharply tuned circuits, would not occur on the steep portion of the curve, and so would not have to be taken into account. The desired components of the oscillations in the tuned circuits would then be detected and utilized, as previously described for the unmodulated carrier wave.

Fig. 2 shows the electromagnet 66 attached to the arm 103, of a variable inductance instead of the arm 71 of the variable capacity 7, shown in Fig. 1. The two coils 93 and 94 constitute an inductometer which is connected to the vacuum tube 5. Coil 93 is connected between the grid 98 and the filament 99, and the coil 94 is connected between the filament 99 and the plate 100. The two coils, therefore, provide a feed-back connection between the output circuit and the input circuit of the tube, thereby allowing the tube in connection with the condenser 101 to generate oscillations. The adjustable coil 94 of the inductometer is attached to the arm 103, which carries the electromagnet 66 adapted to be attracted or repelled by the stationary magnet '73. A flow of current through the electromagnet 66, therefore, causes the arm 103 to move, thereby varying the mutual inductance between the coils upon which the frequency of the oscillations generated depends.

Fig. 3 illustrates the resonance curve for a timed circuit in which the current values, I, have been plotted for various values of the frequency, F, of the impressed oscillations. Assuming that the two tuned circuits 46 and 47 have resonance curves corresponding to this curve, in the case where the unmodulated wave is received, the frequency 9 of those generated oscillations should fall on the steep part of the curve, say at G; in the case when the unmodulated carrier wave is suppressed, the circuits should be such that 91 or gg falls at that point.

The meaning of the term synchronism as used herein is not limited to an exact condition of synchronism, such as is true of a plurality of mechanical alternators running .in parallel but also includes such approximate synchronism as is sufficiently exact for a particular purpose. The various novel features inherent in the invention are defined in the appended claims.

What is claimed is:

1. A system. comprising aplurality of sources of oscillations, each capable of generating oscillations independently of reception of oscillatory energy from the other, one of which is a space discharge generator, and means under the joint control of said sources whereby an increase or decrease in the frequency of one of said sources causes a corresponding increase or decrease in the frequency of theother.

2. Synchronizing means for oscillation generators comprising a movable element,and means under the conjoint control of said generators whereby a change in the frequency of oscillations generated by one thereof produces a movement of said element appropriate to cause a change in the frequency generated by the other thereof.

3. A system comprising a generator of oscillations having a tuned circuit, means for deriving alternating current energy from said generator, means for combining said energy with other alternating current energy, and means whereby the combined energies co-operate to control the tuning of said circuit.

4. A wave receiving station comprising wave receiving means, a local source of waves, an element for changing the frequency of said local source, and means operable by frequency variations independently of energy variations of received waves for causing operative move ments of said element.

5. A receiving system comprising a space discharge oscillation generator, and means operable by received oscillations whereby the frequency of said generator is controlled in accordance with changes in the frequency of the received oscillations.

6. A signal receiving system comprising a Jun Hlii

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frequency of the oscillations vacuum tube oscillation generator capable of generating oscillations independently of frequency controlling energy from an external source, and means operable by received oscillations whereby the said generator is caused to generate oscillations of a. frequency having an approximately constant relation to the frequency of the received oscillations.

7. A wave receiving station comprising a pair of input paths for the reception of incoming energy, and means for supplying at least one component of locally produced modulated oscillations to each of said paths.

8. A system comprising an oscillation generator, another source of oscillatory currents, means for deriving electrical ener y from said generator, and means conjoint y operable by energy from said generator and energy derived from said source to cause the produced by said generator to vary substantially simultaneously with and in accordance with variations in the frequencyof the oscillations of said source.

9-. A system comprising an oscillation generator, another source of oscillatory currents, means for deriving energy from said generator, and means conjointly operable by the I derived energy and other energy from said source to cause .the frequency of oscillatlons produced by said generator to bear a fixed relation to the frequency of the, oscillations of said source. O

10. A receiving system comprising a local source of oscillations, control means therefor, a pair of circuits for rece1v1ng incomlng 12. A wave receiving station comprising a plurality of conductive circuits, means for impressing received oscillations upon at least one of said circuits, means for supplying oscillations of a frequency equal to the sum of two frequencies to one of said circuits, and means for supplying oscillations equal to the diiferenceof said two frequencies to the other of said circuits.

13. A wave receiving station comprising a .conductor for conveying incoming oscillations, a plurality of circuits coupled to said conductor, means for supplying oscillations of a frequency equal to the sum of two frequencies of currents existent in the system to be controlled by the said p and means conjointly operable by energy derived from said source and from said generator for controlling the frequencyt of oscillations produced by said generator.

15. The method of reproducing the modulating wave-form from a modulated carrier wave which comprises utilizing a portion of the energy of said wave for maintaining substantially identical the frequency of a locally generated wave and ,the frequency of. the carrier wave, combining energy derived from said carrier wave with the locally generated en'ergy, and impressing the combined energies upon a wave distorting device.

16. The method of maintaining the frequency ofoscillations generated by a generator including a tuned frequency determining I circuit in a desired relation to the frequency 1 of other oscillations, which comprises combining the generated and the other oscillations and causing a component of the resultant current from said combined oscillations to act upon said circuit to restore the desired relation when it isdeparted from. f

17. The method of synchronizing electrical generators which comprises combining energy produced by each of'said generators, selecting energy of a definite characteristic from the energy resulting from'the combination thereof, and utilizing the selected energy to vary the frequency of one of said generators in accordance with variations in the frequency of the other. 18. The method of controlling mechanism which consists in producing a current of a frequency which is equal to the frequency of a current of a certain value plus the difference of the two other existent frequencies, producing another current whose frequency is equal to the said certain 'value'minus the difference of the two other frequencies and jointly acting upon the mechanism by the currents thus roduced.

19. The method of maintaining a fixedrelation between the frequency of received carrier oscillations and oscillations locally generated at a receiving station, 5 which whereby the frequency difference is brought to the desired relation.

20. The method of synchronizing received carrier oscillations and oscillations locally generated at a receiving. station, which method consists in generating currents which vary wlthlthe difference in the'frequenciesof these oscillations, and in controlling the frc quency of the locally generated oscillations in accordance with said currents, whereby the frequency dillerence is brought to zero.

21. The method of synchronizing received carrier oscillations and oscillations locally generated at a receiving station, which method consists in producing other oscillations of a frequency proportional to the difference between the frequency of the locally generated oscillations and the received carrier oscillations. in detecting said other oscillations, and in controlling the,frequency of the locally generated oscillations by the detected currents.

22. The method of synchronizing oscillations locally generated at a receiving station and received carrier oscillations, which method consists in modulating the locally generated oscillations with oscillations of a lower frequency, in'combining the modulated oscillations with the received carrier oscillations to produce other oscillations of a frequency proportional to the dilference between said oscillations, in detecting said other oscillations, and in controlling the frequency of the locally generated oscillations by the' currents resulting from said detection.

23. In a receiving system, an oscillation generator, means for synchronizing the oscillations from said generator with received carrier oscillations, said means comprising means for generating currents which vary with the difference in frequency of the received carrier and the locally enerated two oscillations, magnetic means adapted to control the frequency of the oscillations of said generator, and means for controlling said received carrier oscillations,

ductor for receiving carrier magnetic means by said currents.

24. In a receiving system, a receiving conductor for receiving carrier oscillations, an oscillation generator, means for synchronizing the oscillations from said generator and the received carrier oscillations, said means comprising means for producing other oscillations which increase withincrease in the difference between the frequencies of the oscillations from the said generator and the means for producing other oscillations which decrease with increase in the difference between the frequencies of the oscillations from the said generator and the received carrier oscillations, and means -whereby the oscillations from said generator may be controlled by said other oscillations.

25. In a receiving system, a receiving conoscillations, an oscillation generator, means for producing other oscillations which increase with increase in the difference between the frequencies of the oscillations from said generator andthe received carrier oscillations,

' means for producing other oscillations which decrease with increase in the difi'erence'between the frequencies of the oscillations from said generator and the received carrier oscillations, two ma etic means adapted to control the oscillations of said generator, means for energizing one of said magnetic means with direct currents proportional to the intensity of one of said other oscillations, means for energizing the other of said magnetic means with direct currents proportional to the intensity of the other of said other oscillations, whereby the relation between the frequencies of the oscillations of said generator and the received carrier oscillations may be controlled. 26. In a receiving system, a conductor for receiving carrier oscillations, an oscillation generator, a second oscillation generator, means for modulating the oscillations from said first generator with the oscillations from said second generator, means for combining these modulated oscillations with the received carrier oscillations to produce other oscillations, means for controlling the oscillations of said first generator by said other oscillations, whereby the relation between the oscillations of said first generator and the received carrier oscillations may be controlled.

27. In a receiving system, a conductor for receiving carrier oscillations, an oscillation generator comprising an evacuated vessel and a tuned circuit associated therewith,

means for producing other oscillations of a frequency proportional to the difference in frequency between the oscillations of said generator and the received carrier oscillations, means for controlling the tuning of said circuit in accordance with said other oscillations, whereby the oscillations of said generator may be synchronous with the carrier oscillations.

28. In a receiving system, a conductor for receiving carrier oscillations, an oscillation generator comprising an evacuated vessel and a tuned circuit associated therewith, means for producing other oscillations of a frequency proportional'to the difference in frequency between the oscillations of said generator and the received carrier. oscillations, means for detecting. said other oscillations, electromagnetic means energized by the currents resulting from said detection, and means whereby said electromagnetic means may control the tuning of said circuit.

29. In a receiving system, a conductorfor receiving carrier oscillations, an oscillation generator comprising an evacuated vessel and a tuned circuit associated therewitlnmeans for producing other oscillations of a frequency proportional to the difference in frequencybetween the oscillations of said generator and the received carrier oscillations, means for detecting said other oscillations, two electroarm by the differential action of the two just mentioned electromagnets.

30. An oscillation generator comprising an electron discharge device and appropriate circuit arrangements for translating the energy of unidirectional currents into oscillatory currents, a frequency-determining de-" vice for said currents, and means automatically operable by departure of the produced currents from adesired frequency to positively affect said frequency-determining device in a manner tending to restore the frequency.

31. A system for controlling the frequency of waves generated by an electron discharge device having frequency determining means comprising a'circuit for receiving a portion of the wave energy generated by said device, and positively acting devices connected to said circuit and said device for affecting said frequency determining 'means in accordance with variations in the produced waves.

32. A thermionic generator and frequency-- I control means therefor comprising a tuned circuit, means controlled bysaid generator for supplying current to'said circuit of such a frequency that a small change in frequency produces a large change of current in said circuit, and positively acting means operable by the current in said circuit for actively controlling the frequency of said generator.

33. A thermionic generator and frequencycontrol means therefor comprising a pair of tuned circuits, means controlled by said generator for supplying current to said circuits of such a frequency that a-small change in frequency produces large changes of current in-said circuits, and positively acting means operable by the changes of current in said circuits for restoring the frequency of said generator t-O a normal value.

34. Means for the production of carrier frequency oscillations comprising a self-oscillatory thermionic discharge generator, an electron discharge tube having an anode, a cathode, and a control element, an input cir- .cuit connected to said element and an output circuit connected to said anode, means for applying to said input circuit current which varies with variations in characteristic of the generated oscillations, and means operatively associating said output circuit'with said generator for acting thereon responsive to variations'of current supplied to said input circuit.

35. Means for controlling the output of an electrical generator of relatively high frequency comprising means for producing elections of numerical trical waves of relatively low frequency from the waves produced by said generator, means whereby variations in the waves produced by said high frequency generator produce variamagnitude equal thereto in said low frequency waves, and' means controlled by said low frequency waves to control said high frequency generator.

36. A control system for an electrical wave producing device comprising means. for deriving from the waves produced by said device other waves of different frequency, arrangementswhereby small percentage changes in frequency of waves from said device cause large percentage changes in the derived waves, and controlling instrumentalities actuated by changes in frequency of said derived waves for acting on said device.

37. The combination of an electrical device with control means therefor, said control means comprising an auxiliary device for supplying controlling alternating current to an electron discharge device, instrumentalities controlled by variations in said electrical device to cause variations in energy supplied to said discharge device by said auxiliary device, and means whereby said discharge device controls said electrical device.

38. A receiving system comprising means for receiving a signal modified high-frequency wave. means for utilizing the energy of said wave to synchronize a local source of waves, and means for combining energy of said wave with wave energy from said local source to produce low frequency variations suitable for operating an indicating instrument.

89. The method of receiving which comprises locally combining wave energy of two locally controlled frequencies to produce a combination frequency, selecting the combination frequency and combining it with en-, ergy received from a remote station.

40. The method which comprises modulating one locally'produced current by another locally produced current to produce combination frequency currents and separately combining said combination frequency cur- 1 rents with currents derived from the energy Iii) oscillation of slightly variable frequency, whereby said oscillations automatically remain in synchronism, maintaining synchronism between the local oscillation and said externally impressed signal oscillation, combining said oscillations, and detecting the voice modulation of the combined oscillations.

43. The method of receiving radio signals whose amplitude of oscillation varies at audio frequency, which comprises providing a separately generated local oscillation continuously maintained and capable of having its frequency readily changed through small amounts by an externally impressed signal oscillation of slightly variable frequency, whereby said oscillations automatically remain in synchronism, maintaining synchroism between the local oscillation and the impressed oscillation, combining said oscillations, and detecting the audio-frequency variation of the combined oscillations.

44. In a receiving system, an oscillation generator, means for maintaining a fixed relation between the frequency of the oscillations from said generator and received carrier oscillations, said means comprising means for generating currents which vary with the amount these frequencies differ from said fixed relation, and means for causing said currents to change the frequency of the oscillations of said generator, whereby the difference between the frequencies is brought to the desired relation. I

45. In a receiving system, an oscillation generator. means for synchronizing the oscillations of said generator with received carrier oscillations, said means comprising means for generating currents which vary with the difi'erence in frequency of the received carrier and the locally generated oscillations, and means for causing said currents to change the frequency of the oscillations of said generator, whereby the difi'erence between the oscillations is brought to zero;

4-6. In a receiving system, an oscillation generator, means for synchronizing the oscillations from said generator with received carrier oscillations, said means comprising means for generating currents which vary with the difference in frequency of the received carrier and the locally generated oscillations, magnetic means adapted to control the frequency of the oscillations of said generator, and means for controlling said magnetic means by said currents.

In witness whereof I hereunto subscribe my name this 28th day of August, A. D., 1917.

RALPH V. L. HARTLEY. 

